The present invention relates to a new and improved construction of a cooled wall, especially for gas turbine elements, which is of the type comprising an outer plate and an inner plate, for instance formed of sheet metal, between which there flows a cooling agent. The invention also pertains to the use of the novel cooled wall of this development.
With the present day conventional high-temperature gas turbines the individual gas turbine elements, such as blading, thermal dam-up segments, combustion chambers and infeed channels, are predominantly cooled by means of air. At the individual components there are provided cooling air channels through which flows the cooling air and slots and openings through which again exits such air. Thus, for instance, there is blown-off at the blading of a gas turbine part of the cooling air at the outflow edges. The arrangement of cooling air channels in the components requires relatively large wall thicknesses thereof, with the result that at such components or parts there are formed correspondingly great thermal stresses which are effective both in the lengthwise and also transverse direction thereof. These thermal stresses arise both during the non-static and static operation and lead to pronounced thermal loads or stress and can cause fracture of the component or part.
With heretofore known constructions, for instance according to the teachings of U.S. Pat. No. 3,446,481, the aforementioned components or parts are fabricated by precision casting. However, there also are partially used sheet metal constructions in order to maintain the thermal stresses small. In such case the smooth thin outer wall is welded to a corrugated or undulated sheet metal plate serving as the inner wall, to thus form cooling channels for the cooling agent.
However, what is disadvantageous with this state-of-the-art construction is that the corrugated plate serving as the inner wall is only elastic in one direction, so that it expands in conjunction with the hot outer wall in such direction. On the other hand, in the other directions there remains the elongation differences between the hot outer wall and the cool inner wall, and thus considerable thermal stresses appear in such directions.
Since when working with higher gas temperatures there is necessary a pronounced cooling, there is required during the use of air as the cooling agent for the high heat-transfer coefficient at the side of the cooling air also high flow velocities, whereby there results high pressure losses. In such instances it is possible to employ instead of air cooling a vapor or liquid cooling. This cooling system is constructed for instance in a manner such that a massive bucket core is provided at the outer contour thereof with milled or machined portions for receiving cooling agent channels, preferably constituted by tubes, and the tubes are clad with an outer covering. Significant in this regard is German patent publication No. 2,825,801.
However, what is disadvantageous with this arrangement is that the blading or bucket core must be of massive design and must be connected with the outer wall, so that greater thermal stresses exist. A design resorting to embedding of the lines through which there is conducted the liquid in copper would only inappreciably reduce such thermal stresses.